PROJECT SUMMARY Harmful alcohol use remains a serious public health issue, resulting in 3 million global deaths per year and contributing to more than 200 disease and injury conditions. Within the United States, the prevalence of Alcohol-use Disorder (AUD) has increased significantly, from 8.5% to 12.7% over the last 10 years and whose complex etiology has limited the number of effective therapeutics currently available. An interesting phenomenon in alcohol drinking is the variability of consumption occurring within the human population: some individuals drink casually while others drink in an uncontrolled manner, escalating their consumption and eventually developing alcohol dependence. To understand the circuit-specific functions underlying this phenomenon of individual alcohol drinking variability, we utilized isogenic C57BL/6J mice, an inbred mouse strain typically used to study alcohol-drinking behaviors. This mouse model provides the unique opportunity to investigate the neurophysiological mechanisms underlying low and high alcohol drinking behaviors, independent of genetics. Furthermore, it is known that a hallmark of the progression of AUD is the dysfunction of dopamine (DA) neurons projecting from the ventral tegmental area to (VTA-NAc) the nucleus accumbens, an area critical to encoding the salience of both drug and naturalistic stimuli. Using in vivo fiber photometry calcium imaging and in vivo electrophysiological recordings, we are now able to determine the neural population response of the VTA-NAc DA circuit before and after the establishment of alcohol drinking phenotype, to illuminate the transition to healthy or unhealthy alcohol drinking profiles. Our preliminary data show that the magnitude of the primary reinforcing VTA-NAc DA response to rewarding and salient stimuli correlates with future establishment of alcohol preference (Aim 1). Further, alcohol-induced neuroadaptations differentially affect naturalistic behaviors in mice, including exploration and response to reward, and cause heightened or blunted responses to alcohol (Aim 2). By assessing the VTA-NAc DA neuronal profile of activity during naturalistic mammalian behaviors prior to and after alcohol exposure, this project will provide novel insight into physiological and real-time predictors of future, individual alcohol drinking and how alcohol actively and reciprocally attenuates or exacerbates VTA-NAc DA circuit function, leading to subsequent maladaptive behaviors.